1. Field of the Invention
The present invention generally relates to an image display system, an image display method and a program, which are for displaying an image, and more specifically, to an image display system, an image display method and a program that improve quality of an image moving on a display.
2. Description of the Related Art
In recent years, among display devices, a liquid crystal display (LCD) provided with thin film transistors (TFT) has continued to develop greatly from viewpoints of its reduction in weight, thinness, portability, low power consumption and so on. Such an LCD is a display utilizing a property of liquid crystals, in which a molecular alignment is changed by applying a predetermined voltage thereto.
Moreover, an organic light emitting diode (OLED) (also called “an organic EL”) has attracted attention as a next-generation display device. The OLED is a device for emitting light by flowing a direct current through a fluorescent organic compound excited by applying an electric field thereto. The OLED is thin, can achieve a wide viewing angle and be used for a wide variety of applications.
For example, though an LCD for use in a PC has been mainly used for displaying a still image heretofore, the LCD has become widely used in place of a cathode ray tube (CRT) such as for displaying a motion picture as a graphics system and displaying a video image as a monitor and the like. In this connection, the technology of displaying a motion picture on the LCD has attracted attention increasingly. Moreover, with the OLED, the necessity of improving motion picture quality is high.
In the case of displaying a motion picture in such a manner, in the display devices other than an impulse-type display such as the CRT, several defects occur with regard to an object in motion due to an effect of a so-called “light-stimulus integration” (properties of an afterglow reflected on a human retina when following a motion picture).
Such defects include a blur of the front edge, a tailing of the rear edge, a lowering of the brightness, and a delay of the perceived position on the front edge or a center position.
Here, the LCD is a hold-type apparatus in which light is continuous for the entire period of a frame, and in terms of the motion picture quality, the LCD cannot follow the CRT as it is.
For example, in a TFT-LCD of a current twisted nematic (TN) mode, the response time of ON/OFF is approximately one refresh cycle (16.7 ms at a 60 Hz refresh rate). Such a response time is much slower than the response time of the CRT, which is almost zero (0).
In this connection, there is a so-called “overdrive technology” as one of the improvements in the response time in the LCD. In order to improve the response characteristics of the LCD to a step input, this overdrive technology applies a higher voltage than a target voltage for the step input in the first frame where the input is changed, and accelerates transition of the brightness. The use of this overdrive technology reduces the response time to one frame or less, and brings the display quality of the LCD close to the quality of a so-called “complete-hold-type” (of which response time is close to zero). The above-described OLED corresponds to this complete-hold-type display.
FIGS. 9(a) and 9(b) are diagrams for explaining the light-stimulus integration in the complete-hold-type display.
FIG. 9(a) shows a state where the object 301 having the brightness V and the width W (pixels) moves at the moving speed S (S pixels per frame) in a screen coordinate system. In this case, the moving speed of the sight that follows the object is also S.
In FIG. 9(a), the axis of ordinates represents times and shows a state where the object 301 moves in the left-to-right direction to the time 0 taking a time for two frames (here, 33.3 ms) and further moves for one frame (16.7 ms) before the start of the next frame. In the example shown in FIGS. 9(a) and 9(b), the moving speed S is larger than the width W. Specifically, the relation W/S≦1 is established.
FIG. 9(b) shows a light-stimulus integration in this case, in which the axis of ordinates represents brightness and the axis of abscissas represents a retinal coordinate system. When the time is zero (0), a brightness of pixels (S−W) among the entire pixels (S+W) is represented as: V·{W/S} with respect to the original brightness V. The brightness gradually increases before the pixels (S+W) and gradually decreases thereafter. The front edge from which the brightness gradually increases becomes blurred, and the rear edge to which the brightness gradually decreases becomes tailed (e.g., tails off). Moreover, there occurs a center delay of S/2 for a position in the screen coordinate system at the time of starting the next frame.
Specifically, even if the complete-hold-type is used, the object with the width W expands to S+W in the retinal coordinate system when moving at the moving speed S. Moreover, there occur the lowering of the brightness, the delay of the perceived position, the blur of the front edge, and the tailing of the rear edge.
Moreover, in order to bring the display device such as an LCD and an OLED close to the impulse type such as the CRT from the complete-hold-type display, a so-called “blanking system” is suitably used, in which light is emitted intermittently for each frame, and a light emitting time is reduced.
However, for example with regard to the OLED, the light emission efficiency is low, and the brightness is lowered if the blanking is employed therefor, thereby lowering the contrast.